diff --git a/Documentation/Filters/Database-Firewall-Filter.md b/Documentation/Filters/Database-Firewall-Filter.md
index bb801bdc6..7c3401919 100644
--- a/Documentation/Filters/Database-Firewall-Filter.md
+++ b/Documentation/Filters/Database-Firewall-Filter.md
@@ -88,6 +88,9 @@ action=block
 rules=/home/user/blacklist-rules.txt
 ```
 
+If a query is blocked, the filter will return an error to the client with the
+error number 1141 and an SQL state of HY000.
+
 #### `log_match`
 
 Log all queries that match a rule. For the `any` matching mode, the name of the